Organic line width roughness with H2 plasma treatment

ABSTRACT

A method for reducing very low frequency line width roughness (LWR) in forming etched features in an etch layer disposed below a patterned organic mask is provided. The patterned organic mask is treated to reduce very low frequency line width roughness of the patterned organic mask, comprising flowing a treatment gas comprising H 2 , wherein the treatment gas has a flow rate and H 2  has a flow rate that is at least 50% of the flow rate of the treatment gas, forming a plasma from the treatment gas, and stopping the flow of the treatment gas. The etch layer is etched through the treated patterned organic mask with the reduced very low LWR.

BACKGROUND OF THE INVENTION

The present invention relates to the formation of semiconductor devices.

During semiconductor wafer processing, features of the semiconductordevice are defined in the wafer using well-known patterning and etchingprocesses. In these processes, a photoresist (PR) material is depositedon the wafer and then is exposed to light filtered by a reticle. Thereticle is generally a glass plate that is patterned with exemplaryfeature geometries that block light from propagating through thereticle.

After passing through the reticle, the light contacts the surface of thephotoresist material. The light changes the chemical composition of thephotoresist material such that a developer can remove a portion of thephotoresist material. In the case of positive photoresist materials, theexposed regions are removed, and in the case of negative photoresistmaterials, the unexposed regions are removed. Thereafter, the wafer isetched to remove the underlying material from the areas that are nolonger protected by the photoresist material, and thereby define thedesired features in the wafer.

SUMMARY OF THE INVENTION

To achieve the foregoing and in accordance with the purpose of thepresent invention, a method for reducing very low frequency line widthroughness (LWR) in forming etched features in an etch layer disposedbelow a patterned organic mask is provided. The patterned organic maskis treated to reduce very low frequency line width roughness of thepatterned organic mask, comprising flowing a treatment gas comprisingH₂, wherein the treatment gas has a flow rate and H₂ has a flow ratethat is at least 50% of the flow rate of the treatment gas, forming aplasma from the treatment gas, and stopping the flow of the treatmentgas. The etch layer is etched through the treated patterned organic maskwith the reduced very low LWR.

In another manifestation of the invention a method for reducing very lowfrequency line width roughness (LWR) in forming etched features in aconductive layer disposed below a hard mask layer disposed below an etchlayer disposed below a patterned photoresist mask forming a stack on awafer is provided. The wafer is placed in a process chamber. Thepatterned photoresist mask is treated to reduce very low frequency linewidth roughness of the patterned photoresist mask, comprising flowing atreatment gas comprising H₂, wherein the treatment gas has a flow rateand H₂ has a flow rate that is at least 50% of the flow rate of thetreatment gas into the process chamber, forming a plasma from thetreatment gas, and stopping the flow of the treatment gas. The etchlayer is etched through the treated patterned photoresist mask. The hardmask layer is etched through the etched layer. The conductive layer isetched through the hard mask layer. The wafer is removed from theprocess chamber, so that the treating the patterned organic mask,etching the etch layer, etching the hard mask layer, and etching theconductive layer are all done in situ in the same process chamber.

In another manifestation of the invention an apparatus for reducing verylow frequency line width roughness (LWR) in forming etched features inan etch layer, disposed below a patterned organic mask with maskfeatures is provided. A plasma processing chamber is provided,comprising a chamber wall forming a plasma processing chamber enclosure,a substrate support for supporting a wafer within the plasma processingchamber enclosure, a pressure regulator for regulating the pressure inthe plasma processing chamber enclosure, at least one antenna forproviding inductively coupled power to the plasma processing chamberenclosure for sustaining a plasma, a gas inlet for providing gas intothe plasma processing chamber enclosure, and a gas outlet for exhaustinggas from the plasma processing chamber enclosure. A gas source is influid connection with the gas inlet and comprises an etchant gas sourceand a H₂ treatment gas source. A controller is controllably connected tothe gas source and the at least one antenna and comprises at least oneprocessor and computer readable media. The computer readable mediacomprises computer readable code for treating the patterned organic maskto reduce very low frequency line width roughness of the patternedorganic mask, comprising computer readable code for flowing a treatmentgas comprising H₂, wherein the treatment gas has a flow rate and H₂ hasa flow rate that is at least 50% of the flow rate of the treatment gas,computer readable code for forming a plasma from the treatment gas, andcomputer readable code for stopping the flow of the treatment gas, andcomputer readable code for etching the etch layer through the treatedpatterned organic mask with the reduced very low LWR.

These and other features of the present invention will be described inmore detail below in the detailed description of the invention and inconjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a high level flow chart of a process that may be used in anembodiment of the invention.

FIGS. 2A-C are schematic cross-sectional views of a stack etchedaccording to an embodiment of the invention.

FIG. 3 is a schematic view of a plasma processing chamber that may beused in practicing the invention.

FIGS. 4A-B illustrate a computer system, which is suitable forimplementing a controller used in embodiments of the present invention.

FIGS. 5A-F are CD-SEMs of wafers processed by examples of embodiments ofthe invention.

FIGS. 6A-C are graphs of results from the above examples of embodimentsof the invention.

FIG. 7 is a CD-SEM (top-down) of a wafer with a mask that illustratesLWR.

FIG. 8 shows a typical sequence that is followed to obtain the LWR vsinspect length curve.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference toa few preferred embodiments thereof as illustrated in the accompanyingdrawings. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art, thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well known process steps and/orstructures have not been described in detail in order to notunnecessarily obscure the present invention.

To facilitate understanding, FIG. 1 is a high level flow chart of aprocess that may be used in an embodiment of the invention, whichreduces very low frequency line width roughness below a patternedphotoresist mask. A wafer with a patterned photoresist mask is placedinto an inductively coupled TCP chamber (step 102). The patternedphotoresist mask is treated to reduce very low frequency line widthroughness (LWR) (step 104). This step comprises flowing a H₂ treatmentgas into a process chamber (step 108), forming a plasma from the H₂treatment gas (step 112), which reduces the very low frequency linewidth roughness. Subsequent processing steps may be performed tocomplete the structure. The flow of the H₂ treatment gas is stopped(step 116) to stop the treatment process. For example, in one embodimentan etch layer is etched (step 120) after the PR treatment. In thisembodiment, the etch layer is an organic ARC layer, which is above ahard mask layer, which is above a conductive layer. The hard mask isthen opened (step 124). The conductive layer is etched (step 128). Thewafer is removed from the process chamber (step 132).

Example

In an example of an implementation of the invention, a wafer is providedwith an etch layer and a photoresist mask. FIG. 2A is a cross-sectionalview of an example of a wafer 204 over which a conductive layer 208 isformed, over which a hard mask layer 212 is formed, over which anorganic antireflective coating (ARC) layer 216 is formed, over which apatterned PR mask 220 is formed. In this example, the patterned PR mask220 is of a 193 nm or higher generation photoresist material. Theorganic ARC layer 216 may be a BARC (bottom antireflective coating)material. The hard mask layer 212 may be one or more layers of differentmaterials, such as SiO_(x) or SiN_(x). The conductive layer 208 is of aconductive material such as polysilicon, amorphous silicon, or a metalsuch as TiN. In this example, the wafer 204 is a crystalline siliconwafer.

In this example, the patterned photoresist mask 216 has a very lowfrequency line edge roughness. A very low frequency line width roughnessrepetition length of greater than 500 nm. More preferably, the very lowline edge roughness repetition length is greater than 550 nm. Line widthroughness is the 3 a value of line width in a given inspection area,which may be calculated according to:

$\begin{matrix}{{LWR} = {3 \times \sqrt{\frac{\sum\limits_{i = 1}^{n}\;\left( {{CD}_{i} - \overset{\_}{CD}} \right)^{2}}{n - 1}}}} & \left( {{Equation}\mspace{20mu} 1} \right)\end{matrix}$

FIG. 7 is a CD-SEM (top-down) of a wafer with a mask 704 thatillustrates LWR. An inspection length 708 is selected. Along theinspection length, line widths 712 are measured for a feature extendingalong the inspection length. The measured line widths 712 are used inequation 1 to calculate LWR.

FIG. 8 shows a typical sequence that is followed to obtain the LWR vsinspect length curve. Following image acquisition from the CD-SEM(top-down), at the optimal focus, beam alignment, and integration, anoptimal LWR algorithm is applied to relevant features in the image. Thevariation of LWR is studied as a function of inspect length and theresult is a curve that shows the high- and very low-frequency LWRcomponents. The regions where the LWR curve flattens out (at twolocations, inspect length ˜200 nm and ˜600 nm) correspond to theamplitudes of the high- and very low-frequency LWR, respectively.

The wafer 204 is placed in an inductively coupled plasma processingchamber (step 102).

FIG. 3 illustrates a processing tool that may be used in animplementation of the invention. FIG. 3 is a schematic view of a plasmaprocessing system 300, including a plasma processing tool 301. Theplasma processing tool 301 is an inductively coupled plasma etching tooland includes a plasma reactor 302 having a plasma processing chamber 304therein. A transformer coupled power (TCP) controller 350 and a biaspower controller 355, respectively, control a TCP power supply 351 and abias power supply 356 influencing the plasma 324 created within plasmachamber 304.

The TCP power controller 350 sets a set point for TCP power supply 351configured to supply a radio frequency signal at 13.56 MHz, tuned by aTCP match network 352, to a TCP coil 353 located near the plasma chamber304. An RF transparent window 354 is provided to separate TCP coil 353from plasma chamber 304 while allowing energy to pass from TCP coil 353to plasma chamber 304.

The bias power controller 355 sets a set point for bias power supply 356configured to supply an RF signal, tuned by bias match network 357, to achuck electrode 308 located within the plasma chamber 304 creating adirect current (DC) bias above electrode 308 which is adapted to receivea substrate 306, such as a semi-conductor wafer work piece, beingprocessed.

A gas supply mechanism or gas source 310 includes a source or sources ofgas or gases 316 attached via a gas manifold 317 to supply the properchemistry required for the process to the interior of the plasma chamber304. A gas exhaust mechanism 318 includes a pressure control valve 319and exhaust pump 320 and removes particles from within the plasmachamber 304 and maintains a particular pressure within plasma chamber304.

A temperature controller 380 controls the temperature of a coolingrecirculation system provided within the chuck electrode 308 bycontrolling a cooling power supply 384. The plasma processing systemalso includes electronic control circuitry 370. The plasma processingsystem may also have an end point detector.

FIGS. 4A and 4B illustrate a computer system 400, which is suitable forimplementing a controller for control circuitry 370 used in embodimentsof the present invention. FIG. 4A shows one possible physical form ofthe computer system. Of course, the computer system may have manyphysical forms ranging from an integrated circuit, a printed circuitboard, and a small handheld device up to a huge super computer. Computersystem 400 includes a monitor 402, a display 404, a housing 406, a diskdrive 408, a keyboard 410, and a mouse 412. Disk 414 is acomputer-readable medium used to transfer data to and from computersystem 400.

FIG. 4B is an example of a block diagram for computer system 400.Attached to system bus 420 is a wide variety of subsystems. Processor(s)422 (also referred to as central processing units, or CPUs) are coupledto storage devices, including memory 424. Memory 424 includes randomaccess memory (RAM) and read-only memory (ROM). As is well known in theart, ROM acts to transfer data and instructions uni-directionally to theCPU and RAM is used typically to transfer data and instructions in abi-directional manner. Both of these types of memories may include anysuitable of the computer-readable media described below. A fixed disk426 is also coupled bi-directionally to CPU 422; it provides additionaldata storage capacity and may also include any of the computer-readablemedia described below. Fixed disk 426 may be used to store programs,data, and the like and is typically a secondary storage medium (such asa hard disk) that is slower than primary storage. It will be appreciatedthat the information retained within fixed disk 426 may, in appropriatecases, be incorporated in standard fashion as virtual memory in memory424. Removable disk 414 may take the form of any of thecomputer-readable media described below.

CPU 422 is also coupled to a variety of input/output devices, such asdisplay 404, keyboard 410, mouse 412, and speakers 430. In general, aninput/output device may be any of: video displays, track balls, mice,keyboards, microphones, touch-sensitive displays, transducer cardreaders, magnetic or paper tape readers, tablets, styluses, voice orhandwriting recognizers, biometrics readers, or other computers. CPU 422optionally may be coupled to another computer or telecommunicationsnetwork using network interface 440. With such a network interface, itis contemplated that the CPU might receive information from the network,or might output information to the network in the course of performingthe above-described method steps. Furthermore, method embodiments of thepresent invention may execute solely upon CPU 422 or may execute over anetwork such as the Internet in conjunction with a remote CPU thatshares a portion of the processing.

In addition, embodiments of the present invention further relate tocomputer storage products with a computer-readable medium that havecomputer code thereon for performing various computer-implementedoperations. The media and computer code may be those specially designedand constructed for the purposes of the present invention, or they maybe of the kind well known and available to those having skill in thecomputer software arts. Examples of tangible computer-readable mediainclude, but are not limited to: magnetic media such as hard disks,floppy disks, and magnetic tape; optical media such as CD-ROMs andholographic devices; magneto-optical media such as floptical disks; andhardware devices that are specially configured to store and executeprogram code, such as application-specific integrated circuits (ASICs),programmable logic devices (PLDs) and ROM and RAM devices. Examples ofcomputer code include machine code, such as produced by a compiler, andfiles containing higher level code that are executed by a computer usingan interpreter. Computer readable media may also be computer codetransmitted by a computer data signal embodied in a carrier wave andrepresenting a sequence of instructions that are executable by aprocessor.

The patterned PR mask 220 is treated to reduce very low frequency linewidth roughness (step 104). This is accomplished by first flowing atreatment gas comprising H₂ into the process chamber, where thetreatment gas has a flow rate and the H₂ has a flow rate that is atleast 50% of the flow rate of the treatment gas. Preferably, thetreatment gas consists essentially of H₂ and Ar. More preferably, thetreatment gas consists essentially of H₂. The treatment is formed into aplasma using a low bias (step 112). Preferably, the bias voltage for thelow bias is between 0 to 100 volts. More preferably, the bias voltagefor the low bias is between 0 to 50 volts. Most preferably, the biasvoltage for low bias is 0 volts. The flow of the treatment step isstopped (step 116), to end the PR mask treatment.

A specific example of a treatment recipe provides an H₂ treatment gas of100 sccm H₂ and 100 sccm Ar at a pressure of 10 mT. Ranges of thetreatment gas in this example recipe may provide 50-500 sccm H₂ and0-500 sccm Ar, at pressures between 2-40 mT. The power provided to forma plasma from the treatment gas is 200-1500 W at 13.56 MHz. Morespecifically, the power is 1000 W. The bias voltage is 0 volts. Anelectrostatic chuck temperature of 60° C. is provided. The treatmentprocess is maintained for 5-60 seconds.

FIGS. 5A-F are CD-SEM (top-down) of wafers of various examples. FIG. 5Ais a CD-SEM of a wafer before treatment. The CD of the wafer is 103.5nm. The very low frequency LWR is 6.1 nm. FIG. 5B is the CD-SEM of thewafer of FIG. 5A after the treatment process. The CD is 119.1 nm with avery low frequency LWR of 3.6 nm. Therefore, the very low LWR wasreduced by the plasma treatment. FIG. 6A is a graph of the LWR reductionby the plasma treatment versus inspection length for the wafer of FIG.5B. The inspection length is related to the LWR frequency.

FIG. 5C is a CD-SEM of another type of wafer before treatment. The CD ofthe wafer is 69.8 nm. The very low frequency LWR is 5.9 nm. FIG. 5D isthe CD-SEM of the wafer of FIG. 5C after the treatment process. The CDis 67.3 nm with a very low frequency LWR of 3.9 nm. Therefore, the verylow LWR was reduced by the plasma treatment. FIG. 6B is a graph of theLWR reduction by the plasma treatment versus inspection length for thewafer of FIG. 5D.

FIG. 5E is a CD-SEM of another type of wafer before treatment. The CD ofthe wafer is 58.1 nm. The very low frequency LWR is 4.2 nm. FIG. 5F isthe CD-SEM of the wafer of FIG. 5E after the treatment process. The CDis 57.1 nm with a very low frequency LWR of 2.8 nm. Therefore, the verylow LWR was reduced by the plasma treatment. FIG. 6C is a graph of theLWR reduction by the plasma treatment versus inspection length for thewafer of FIG. 5F.

The organic ARC layer 216 is then etched (step 120), using aconventional organic ARC open process based on the specific material ofthe etch layer. FIG. 2B is a schematic view of the stack after theorganic ARC layer 216 has been etched. The hard mask layer 212 may besubsequently etched using the patterned PR mask 220 and/or the organicARC layer 216 as a patterned mask. The conductive layer 208 may beetched using a conventional conductive layer etch, using the hard masklayer 212 as a patterned mask (step 128) During these process, thephotoresist mask and organic ARC may be stripped away. FIG. 2C is aschematic view of the stack after the conductive layer 208 and the hardmask 212 have been etched, where the PR mask and organic ARC have beenstripped away. Other processes may be used to further form semiconductordevices. The wafer is then removed from the inductively coupled TCPprocess chamber (step 132). Therefore, this example of the inventionperforms treatment to reduce very low frequency LWR, organic ARC open,hard mask open and conductive layer etch in situ in a single inductivelycoupled plasma process chamber. In this embodiment the organic ARC layer216 is the etch layer that is etched after the H₂ treatment.

Without being bound by theory, it was thought that very low frequencyline edge roughness with a repetition rate greater than 500 nm,preferably 550 nm, in a patterned photoresist mask could not be reduced.It was unexpectedly found that an H₂ plasma treatment with low biasvoltage would reduce very low frequency line width roughness.

Other Embodiments

In other embodiments the H₂ treatment to reduce very low frequency LWRmay be performed on other patterned organic masks. For example, anorganic ARC layer that has been opened using a conventional process mayhave very low frequency LWR. The H₂ treatment may then be applied to theopened organic ARC layer to reduce the very low frequency LWR. In suchan example, instead of the organic ARC layer being the etch layer, thehard mask layer is the etch layer that is etched subsequent to the H₂treatment.

In other embodiment a high bias power may be used during the H₂treatment. In other embodiments the etch layer or other layers under theetch layer may be dielectric layers. Such embodiments may have an ARClayer or may not have an ARC layer or may have one or more additionallayers. Such embodiments may or may not have a conductive layer and/or ahard mask layer. If the etch layer is a dielectric layer, an embodimentmay use a capacitively coupled process chamber instead of an inductivelycoupled process chamber. In other embodiments, the treatment may be donein a different chamber than the etching.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and various substituteequivalents, which fall within the scope of this invention. It shouldalso be noted that there are many alternative ways of implementing themethods and apparatuses of the present invention. It is thereforeintended that the following appended claims be interpreted as includingall such alterations, permutations, and various substitute equivalentsas fall within the true spirit and scope of the present invention.

1. A method for reducing very low frequency line width roughness (LWR)with a roughness repetition length of greater than 500 nm in formingetched features in an etch layer disposed below a patterned organicmask, comprising: treating the patterned organic mask to reduce very lowfrequency line width roughness with a roughness repetition length ofgreater than 500 nm of the patterned organic mask, comprising: flowing atreatment gas comprising H₂, wherein the treatment gas has a flow rateand H₂ has a flow rate that is at least 50% of the flow rate of thetreatment gas; forming a plasma from the treatment gas; and stopping theflow of the treatment gas; and etching the etch layer through thetreated patterned organic mask with the reduced very low LWR.
 2. Themethod, as recited in claim 1, wherein the treatment gas is halogenfree.
 3. The method, as recited in claim 1, wherein the treatment gasconsists essentially of Ar and H₂.
 4. The method, as recited in claim 1,wherein the forming a plasma uses a low bias between 0 and 100 volts. 5.The method, as recited in claim 4, wherein the treatment gas is halogenfree.
 6. The method, as recited in claim 4, wherein the treatment gasconsists essentially of Ar and H₂.
 7. The method, as recited in claim 4,wherein the treatment gas consists essentially of H₂.
 8. The method, asrecited in claim 7, wherein the forming a plasma uses no more than 1500watts of RF power.
 9. The method, as recited in claim 8, wherein the lowbias is between 0 to 50 volts.
 10. The method, as recited in claim 8,wherein the low bias is 0 volts.
 11. The method, as recited in claim 10,wherein the very low frequency LWR of the patterned organic mask aftertreatment is less than the very low frequency LWR before treatment. 12.The method, as recited in claim 11, further comprising: placing a waferwith the etch layer and patterned organic mask in a process chamberbefore the treating the patterned organic mask; and removing the waferfrom the process chamber after etching the etch layer.
 13. The method,as recited in claim 12, wherein the process chamber is an inductivelycoupled TCP process chamber.
 14. The method, as recited in claim 13,wherein the organic mask is a photoresist mask.
 15. A method forreducing very low frequency line width roughness (LWR) with a roughnessrepetition length of greater than 500 nm in forming etched features inan etch layer disposed below a patterned organic mask, wherein a hardmask layer is below the etch layer and a conductive layer is below thehard mask layer, comprising: treating the patterned organic mask toreduce very low frequency line width roughness with a roughnessrepetition length of greater than 500 nm of the patterned organic mask,comprising: flowing a treatment gas comprising H₂, wherein the treatmentgas has a flow rate and H₂ has a flow rate that is at least 50% of theflow rate of the treatment gas; forming a plasma from the treatment gas;stopping the flow of the treatment gas; etching the etch layer throughthe treated patterned organic mask with the reduced very low LWR;etching the hard mask layer, and etching the conductive layer, beforeremoving the wafer from the process chamber, so that the treating thepatterned organic mask, etching the etch layer, etching the hard masklayer, and etching the conductive layer are all done in situ in the sameprocess chamber.
 16. A method for reducing very low frequency line widthroughness (LWR) with a roughness repetition length of greater than 500nm in forming etched features in a conductive layer disposed below ahard mask layer disposed below an ARC layer disposed below a patternedphotoresist mask forming a stack on a wafer, comprising: placing thewafer in a process chamber; treating the patterned photoresist mask toreduce very low frequency line width roughness with a roughnessrepetition length of greater than 500 nm of the patterned photoresistmask, comprising: flowing a treatment gas comprising H₂, wherein thetreatment gas has a flow rate and H₂ has a flow rate that is at least50% of the flow rate of the treatment gas into the process chamber;forming a plasma from the treatment gas; and stopping the flow of thetreatment gas; etching the ARC layer through the treated patternedphotoresist mask; etching the hard mask layer through the ARC layer;etching the conductive layer through the hard mask layer; and removingthe wafer from the process chamber, so that the treating the patternedorganic mask, etching the ARC layer, etching the hard mask layer, andetching the conductive layer are all done in situ in the same processchamber.